The present invention relates to molded plastic articles having a protected metal film on the surface thereof and to a process for manufacturing same. More particularly, the present invention relates to molded plastic articles having on the surface thereof a thin metal film formed by vacuum evaporation and coated with a particular combination of protective layers and to a process for manufacturing such molded plastic articles.
The best way of imparting metallic appearance and feeling to plastics is to form a metal film on their surface. Known hitherto as means for forming such metal film on the surface of plastics are vacuum-evaporation, hot stamping and electroplating. Besides these, such methods as low temperature sputtering, ion plating and spray-plating are also being put into practice. However, all of these methods involve problems in their execution and in the properties of the resultant products and are hardly considered totally satisfactory for forming a metal film on the surface of plastics.
Among these methods the one capable of producing the products having a metal film most strongly attached thereto comprises providing the surface of plastic articles with a chemical plating and then subjecting the chemically plated surface to an electroplating treatment with a metal or alloy such as copper, nickel or chromium. However, this method is economically unattractive in view of its complicated procedure and has many drawbacks including troublesome treatment of the waste electroplating liquid which often creates environmental pollution. A metal film formed by any of the other methods is extremely thin, i.e. within a range from several thousand angstroms to several microns and is weak in intermetallic binding force. Thus, such a thin metal film is extremely poor in resistant properties such as abrasion-resistance and weathering-resistance. In the conventional arts, therefore, the surface of a metal-plated or -coated product should be provided with a protective film, for example, by applying a coating paint onto the surface.
For example, in the case of the method utilizing vacuum evaporation generally adopted among these methods for forming a metal film on the surface of plastic articles, the desired products are produced usually by applying an under paint (called "base coat") onto the surface of molded plastic articles, drying the under paint, applying a metal such as aluminum onto the dried paint surface by vacuum evaporation and then applying a covering paint (called "top coat") functioning as a protective layer onto the surface of the metal film. However, the metal-coated plastic articles obtained according to this method are poor in weather-resisting property and are unsuited for outdoor uses because they undergo degradative ageing or permit peeling of the top coat followed by discoloration or corrosion of the metal film when used outdoors and exposed under various weathering conditions including raining and irradiation of sun beams. At the present time, therefore, the use of the products obtained according to this method are limited exclusively to indoor objects. Especially in the case of thermoplastic plastics which restrict the permissible treatment temperature, a paint of excellent performance which requires baking at a high temperature cannot be used. Further, protective paints utilizable in this case will considerably be limited if their cohesiveness to the metal film is taken into account.
It follows from this that even in the case of producing thermoplastic plastics having a metal film on the surface thereof by means of vacuum evaporation, such plastic products fail to withstand outdoor uses exposed to severe weathering actions. In order to obtain plastic articles having on the surface thereof a metal film tolerant to outdoor uses, there is no way but to manufacture such plastic articles by means of electroplating or painting of a plastic article with a metal or by imbedding in a plastic article a metal film formed by vacuum evaporation and then coated with polyvinyl chloride or an acrylic resin or by providing the reverse side of a plastic article with a metal film by vacuum evaporation or cohesion. However, these methods not only entail high cost but also are disadvantageous in that they make it difficult to select the tint of the products freely and a considerable limitation exists in the aspect of the design of the products. Hence, there is a great demand for developing plastic articles having on the surface thereof a metal film tolerant to outdoor uses.